Oxygenator

ABSTRACT

An oxygenator that inhibits or prevents bubbles in blood from exiting through a blood outlet includes an oxygenator part which performs gas exchange on blood and a heat exchanging part which performs heat exchange on the blood. The oxygenators part has a housing that is generally in a rectangular parallelepiped form, with a hollow fiber membrane bundle positioned in the housing. The hollow fiber membrane bundle is formed by a multiplicity of hollow fiber membranes adapted to perform gas exchange. Blood flows along a blood passage comprised of gaps between the hollow fiber membranes and contacts the surface of the hollow fiber membranes where gas exchange occurs with gas flowing through the lumens of the hollow fiber membranes. In addition, a filter member is arranged on a downstream side of the hollow fiber membrane bundle so that bubbles present in the blood are caught by the filter member.

This application is a divisional of U.S. application Ser. No. 11/654,599filed on Jan. 18, 2007, and claims priority to Japanese Application No.2006-11702 filed on Jan. 19, 2006, the entire content of both of whichis incorporated herein by reference.

TECHNICAL FIELD

The present invention generally relates to an oxygenator and a methodperforming gas exchange for blood.

BACKGROUND DISCUSSION

There are known oxygenators constructed to perform gas exchange by useof a multiplicity of hollow fiber membranes. An example of such anoxygenator is described in U.S. Pat. No. 6,503,451.

This oxygenator includes a housing, a hollow fiber membrane bundlereceived in the housing, blood-inlet and blood-outlet ports, andgas-inlet and gas-outlet ports so that gas exchange (i.e., oxygenationand carbon dioxide removal) is performed between blood and gas throughthe hollow fiber membranes.

In oxygenators constructed in this manner, bubbles may exist in theblood introduced through the blood inlet port. In such a case, bubblesare preferably removed by the hollow fiber membrane bundle.

However, the hollow fiber membrane bundle is specifically designed toefficiently carry out gas exchange, without being specifically intendedto remove bubbles. Thus, there is a problem that bubbles are not fullyremoved by the hollow fiber membrane bundle, with the result thatbubbles remaining in the blood that is discharged from the blood outletport being carried downstream of the oxygenator. For this reason, abubble-removing arterial filter is sometimes provided on an arterialline between the oxygenator and the patient.

SUMMARY

According to one aspect, a method of performing gas exchange for bloodcomprises: introducing blood into a blood inlet of a housing in whichare positioned a plurality of hollow fiber membranes each having a lumenin communication with a gas inlet and a gas outlet so that the bloodflows outside the lumens of the hollow fiber membranes toward a bloodoutlet; introducing gas into the lumens of the hollow fiber membranes tosubject the blood flowing outside the lumens of the hollow fibermembranes to gas exchange; removing bubbles in the blood after the bloodhas been subjected to the gas exchange and before the blood isdischarged form the housing by way of the blood outlet, with theremoving of the bubbles occurring as a result of the blood which hasbeen subjected to the gas exchange passing through a filter member whichhas a planar surface in direct contact with the hollow fiber membranes;and discharging the blood which has been subjected to the gas exchangeand which has passed through the filter member from the housing by wayof the blood outlet.

According to another aspect, a method of performing gas exchange forblood comprises: introducing blood into a blood inlet of a housing inwhich are positioned a plurality of hollow fiber membranes each having alumen in communication with a gas inlet and a gas outlet so that theblood flows outside the lumens of the hollow fiber membranes toward ablood outlet; introducing gas into the lumens of the hollow fibermembranes to subject the blood flowing outside the lumens of the hollowfiber membranes to gas exchange; and catching bubbles in the blood afterthe blood has been subjected to the gas exchange and before the blood isdischarged from the housing through the blood outlet, the bubbles beingcaught by virtue of the blood which has been subjected to the gasexchange passing through a bubble catching filter member. The bubblescaught by the bubble catching filter member enter the lumens of thehollow fiber membranes and are discharged out of the housing by way ofthe gas outlet, and the blood which has been subjected to the gasexchange and which has passed through the bubble catching filter memberis discharged out of the housing by way of the blood outlet.

Another aspect involves a method of performing gas exchange for bloodcomprising Introducing blood into an inlet of a housing in which arepositioned a plurality of hollow fiber membranes each having a lumen incommunication with a gas inlet and a gas outlet so that the blood flowsexteriorly of the hollow fiber membranes toward a blood outlet,introducing an gas into the lumens of the hollow fiber membranes tosubject the blood flowing exteriorly of the hollow fiber membranes togas exchange, discharging the blood which has been subjected to the gasexchange from the housing by way of the blood outlet, and removingbubbles in the blood in the housing before the blood is discharged fromthe housing by way of the blood outlet by passing the blood through abubble filter.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a perspective view of an embodiment of an oxygenator asdisclosed herein.

FIG. 2 is a cross-sectional side view of the oxygenator shown in FIG. 1taken along the line II-II in FIG. 1.

FIG. 3 is a top view, partially in cross-section, of the oxygenatorshown in FIG. 1.

FIG. 4 is an enlarged cross-sectional view of a lower right region(fixing region of a hollow fiber membrane bundle and a filter member) ofthe oxygenator shown in FIG. 2.

DETAILED DESCRIPTION

The description below describes one embodiment of an oxygenatorillustrated in the drawing figures. In FIGS. 1 and 2, the upper side isreferred to as the “upper” side or “above”, the lower side is referredto as the “lower” side or “below”, the left side is referred to the“blood inlet side” or “upstream side”, and the right side is referred toas the “blood outlet side” or “downstream side”.

The illustrated version of the oxygenator 1 is a heat exchanger-equippedoxygenator comprising an oxygenating part 1A that performs gas exchangewith the blood and a heat exchanging part (heat exchanger) 1B thatperforms heat exchange on the blood. By way of example, this oxygenatorcan be set up as a part of a blood extracorporeal circulation circuit.

The oxygenator 1 includes a housing 2 located on the side of theoxygenating part 1A, and a heat exchanger housing 5 located on the sideof the heat exchanger 1B. The housings are preferably united orintegrated together to form a single unitary body.

Describing initially various aspects of the oxygenating part 1A, thehousing 2 is comprised of a cylindrical housing body 21. In theillustrated embodiment, the housing 2 is a rectangular parallelepipedform (inclusive of a substantially rectangular parallelepiped form)possessing a quadrilateral (rectangular or square) shape (hereinafterreferred to as a “rectangular cylindrical housing body”), a first headeror upper lid 22 closing the upper opening of the rectangular cylindricalhousing body 21, and a second header (lower lid) 23 closing the loweropening of the rectangular cylindrical housing body 21. Both the firstheader 22 and second header 23 are a dish-shaped, including aplate-shaped portion with a projecting or upstanding wall extendingaround the periphery of the plate-shaped portion.

The rectangular cylindrical housing body 21, the first header 22 and thesecond header 23 are each formed of a resin material, for examplepolyolefin such as polyethylene or polypropylene, an ester resin (e.g.,polyester such as polyethylene terephthalate or polybutyleneterephthalate), a styrene resin (e.g., polystyrene, MS resin or MBSresin) or polycarbonate, a ceramics material of various kinds or a metalmaterial. The first and second headers 22, 23 are secured in aliquid-tight manner to the rectangular cylindrical housing body 21 by,for example, joining by fusion or an adhesive.

The rectangular cylindrical housing body 21 is formed with a tubularblood outlet port 28 projecting in the lower region (lower half) of theblood outlet side. A tubular gas inlet port 26 projects from the uppersurface of the first header 22. As shown in FIG. 2, a tubular gas outletport 27 projects from the lower surface of the second header 23. The gasinlet port 26 has an intermediate portion bent nearly at a right angleso that the tip portion of the gas inlet port 27 is parallel to theblood outlet port 28.

A hollow fiber membrane bundle 3 is housed or received in the housing 2.The hollow fiber membrane bundle 3 is formed by integrating amultiplicity of hollow fiber membranes 31 serving for gas exchange and afilter member 4 serving for catching bubbles.

As shown in FIG. 4, almost all the hollow fiber membranes 31 forming thehollow fiber membrane bundle 3 are arranged nearly parallel with oneanother. In this case, the hollow fiber membranes 31 are arrangedvertically in the lengthwise direction.

The arrangement pattern, direction, etc. of the hollow fiber membranes31 forming the hollow fiber membrane bundle 3 are not limited to thosementioned. For example, the hollow fiber membrane bundle 3 may be formedas a structure in which the hollow fiber membranes 31 are arrangedhorizontally, may be formed as a structure having points at which thehollow fiber membranes 31 obliquely intersect one another(intersections), may be formed as a structure in which all or part ofthe hollow fiber membranes 31 are arranged in a curved manner, or may beformed as a structure in which all or some of the hollow fiber membranes31 are arranged in a corrugated, helical, spiral or annular manner.

The hollow fiber membranes 31 have opposite ends (upper and lower ends)fixed to the inner surfaces of the rectangular cylindrical housing body21 by way of partitioning walls 8, 9 as shown in FIG. 2. Thepartitioning walls 8, 9 are formed of a potting material, e.g.polyurethane or silicone rubber.

The hollow fiber membrane bundle 3 has widthwise opposite endsrespectively fixed or secured to the inner surfaces of the rectangularcylindrical housing body 21 through a setting member 7 as illustrated inFIG. 3. The setting member 7 may be formed of a material similar to thematerial (potting material) forming the partitioning walls 8, 9 or ofanother material.

A gas inlet chamber 261 is defined by the first header 22 and one of thepartitioning walls 8. Each of the hollow fiber membranes 31 possesses anupper opening that opens to and communicates with the gas inlet chamber261. In addition, a gas outlet chamber 271 is defined by the secondheader 23 and the other partitioning wall 9. The hollow fiber membranes31 each possess a lower opening that opens to and communicates with thegas outlet chamber 271. The hollow fiber membranes 31 each have a lumenextending between the open opposite ends forming a gas passage 32through which gas (oxygen-containing gas) is adapted to flow. The gasinlet port 26 and the gas inlet chamber 261 constitute a gas inletcommunicating with the gas passages 32 at an upstream end of the gaspassages while the gas outlet port 27 and the gas outlet chamber 271constitute a gas outlet communicating with the gas passages 32 at adownstream end of the gas passages.

The hollow fiber membrane bundle 3 is sized to nearly completely fillthe interior of the rectangular cylindrical housing body 21 so that thehollow fiber membrane bundle 3 takes a rectangular parallelepiped form(inclusive of a substantially rectangular parallelepiped form). Due tothis, a relatively high charge efficiency by the hollow fiber membranes31 is available (with less dead space) in the rectangular cylindricalhousing body 21 of similar form, which contributes to the size reductionand performance improvement of the oxygenating part 1A.

The hollow fiber membranes 31 are exposed between the partitioning walls8, 9 within the housing 2. A blood passage 33 is formed exterior of thehollow fiber membranes 31, i.e., at gaps between the hollow fibermembranes 31, allowing blood to flow from left to right in FIG. 2.

A blood inlet aperture (blood inlet space) 24 forms a blood inletpossessing a strip or elongated form extending vertically (nearlyparallel with the arrangement of the hollow fiber membranes 31) at anupstream end of the blood passage 33 (closer to an upstream surface ofthe hollow fiber membrane bundle 3), i.e., in a connection regionbetween the rectangular cylindrical housing body 21 and the heatexchanger housing 5. The housing 2 has an interior in communication withthe interior of the heat exchanger housing 5 through the blood inletaperture 24. This structure allows for relatively efficient transfer ofblood from the heat exchanging part 1B to the oxygenating part 1A.

The blood inlet aperture 24 preferably has a length (vertical length asseen with reference to FIG. 2) equal to or greater than 70% of theeffective length of the hollow fiber membrane 31 (i.e., the lengthbetween the lower face of the partitioning wall 8 and the upper face ofthe partitioning wall 9), with the length of the blood inlet aperture 24preferably being no greater than the effective length of the hollowfiber membrane 31. In the illustrated embodiment, the length of theblood inlet aperture 24 is equal to the effective length of the hollowfiber membrane 31. This disclosed length of the blood inlet aperture 24allows for relatively efficient transfer of blood from the heatexchanging part 1B to the oxygenating part 1A and for gas exchange ofblood in the blood passage 33.

At least in the upstream end of the blood passage 33 (closer to theblood inlet aperture 24), the flow of blood is in a direction nearlyorthogonal to the lengthwise extent or direction of the hollow fibermembranes 31. This also helps contribute to a relatively efficient gasexchange of the blood flowing along the blood passage 33.

At the downstream end of the blood passage 33 (closer to the downstreamsurface of the hollow fiber membrane bundle 3), a gap is formed betweena filter member 4, described in more detail later, and an inner surfaceof the rectangular cylindrical housing body 21. The gap forms a bloodoutlet aperture (blood outlet space) 25. The blood outlet aperture 25Acommunicates with the blood outlet port 28, with the blood outletaperture 25 and blood outlet port 28 forming a blood outlet. The bloodoutlet aperture 25 provides the blood outlet with a space where theblood transmitted through the filter member 4 is to flow toward theblood outlet port 28, thus discharging the blood relatively smoothly.

The hollow fiber membrane bundle 3, the filter member 4 and the bloodpassage 33 are positioned between the blood inlet aperture 24 and theblood outlet aperture 25.

By way of example, the hollow fiber membranes 31 can be fabricated ofporous gas-exchange membranes. The porous hollow fiber membranes can beconfigured to possess an inner diameter of approximately 100-1000 μm, awall thickness of approximately 5-200 μm, preferably 10-100 μm, aporosity of approximately 20-80%, preferably approximately 30-60%, and apore size of approximately 0.01-5 μm, preferably approximately 0.01-1μm.

The hollow fiber membrane 31 is preferably fabricated of a hydrophobicpolymer material, e.g. polypropylene, polyethylene, polysulfone,polyacrylonitrile, polytetrafluoroethylene or polymethyl pentane.Polyolefin resin is preferred, and polypropylene is more preferred.Pores are preferably formed in a wall of the material by, for example,stretching or solid-liquid phase separation.

The hollow fiber membranes 31 of the hollow fiber membrane bundle 3 havea length (effective length) that is not particularly limited, but ispreferably approximately 30-150 mm, more preferably approximately 50-100mm.

The hollow fiber membrane bundle 3 has a thickness (horizontal length inFIG. 2) that is not particularly limited, but is preferablyapproximately 10-100 mm, more preferably approximately 20-80 mm.

Similarly, the width (vertical length in FIG. 3) of the hollow fibermembrane bundle 3 is not particularly limited, but is preferablyapproximately10-100 mm, more preferably approximately 20-80 mm.

The filter member 4 is provided at a position downstream of the hollowfiber membrane bundle 3 (closer to the blood outlet) to thus catchbubbles in the blood flowing along the blood passage 33. The filtermember 4 can be formed as a flat sheet member nearly in a rectangularform (hereinafter referred to as a “sheet”). The filter member 4 isfixed in the housing 2 by being secured at its edges (four sides)through the partitioning walls 8, 9 and the respective setting members7.

The filter member 4 is positioned so that its one surface is in contactwith the downstream surface (closer to the blood outlet portion) of thehollow fiber membrane bundle 3, thus covering nearly all the downstreamsurface. The filter member 4 thus has an increased effective area tothereby make it possible to relatively fully exhibit the capability ofcatching bubbles. Also, by increasing the effective area of the filtermember 4, even if clogging (e.g., adhesion of blood aggregates) occursin a part of the filter member 4, blood flow is not completelyobstructed.

The filter member 4 may be, for example, in a mesh form, or of a wovenfabric, a non-woven fabric or a combination thereof. Of these, the meshform is preferred, with a screen filter being particularly preferred.This makes it possible to capture or stop bubbles more positively whilepermitting the passage of blood more easily.

When the filter member 4 is in the form of a mesh, the mesh size is notlimited, though is usually preferably 80 μm or smaller, more preferablyapproximately 15-60 μm, further preferably 20-45 μm. This makes itpossible to catch comparatively fine bubbles without increasing thepassage resistance to blood, thus providing a relatively high catchefficiency of bubbles (bubble removal capability).

The material from which the filter member 4 is made can be, for example,polyolefin such as polyamide, polyethylene or polypropylene, polyestersuch as polyethylene terephthalate, or polybutylene terephthalate,nylon, cellulose, polyurethane, or an aramid fiber. A particularlypreferred material is polyethylene terephthalate, polyethylene orpolyurethane due to the relatively excellent resistance to bloodclotting and the capability of being less clogged.

The filter member 4 also preferably possesses hydrophilicity. Namely,the filter member 4 preferably is made itself of a hydrophilic materialor has been subjected to a hydrophilizing processing (e.g. plasmaprocessing). This makes it relatively easy to remove bubbles uponpriming the oxygenator 1. Also, when the blood mixed with bubbles passesthrough, it is difficult for the bubbles to pass through, thus improvingthe bubble removal capability of the filter member 4 and positivelypreventing the bubbles from passing out of the blood outlet port 28.

The filter member 4 may be comprised of one sheet (particularly one in amesh form, like a screen filter) or two or more sheets.

As described above, a gap (i.e., blood outlet aperture 25) existsbetween the filter member 4 and the housing 2 as seen in FIGS. 2 and 3.This helps prevent the filter member 4 from coming into direct or closecontact with the inner surface of the housing 2. The blood passing thefilter member 4 is allowed to relatively easily and smoothly flow downthe blood outlet aperture 25 and then to the blood outlet port 28.

The filter member 4 is rectangular (or square) in plan in theillustrated embodiment. However, the plan form of the filter member 4 isnot limited to such shape and may instead be trapezoidal, parallelogram,elliptic or oval, for example.

By arranging the filter member 4 in the described manner, even whenbubbles exist in the blood flowing along the blood passage 33, suchbubbles can be caught, thereby preventing the bubbles from going out ofthe blood outlet port 28. This eliminates the necessity of an arterialfilter conventionally provided on the arterial line.

The bubbles, caught by the filter member 4, stay on the upstream side ofthe filter member 4 where they are able to pass into the lumens (gaspassages 32) of the hollow fiber membranes 31 through the multiplicityof fine pores formed in the wall of the hollow fiber membranes 31 wherethey are discharged at the gas outlet port 27, together with the gasflowing the gas passage 32. This eliminates the need for an arterialfilter, thus reducing the priming time upon start of using theoxygenator and preventing the adverse effect caused due to the bubblesstaying in the blood passage 33 (e.g. lowered gas-exchange capability ofthe hollow fiber membrane bundle 3).

The heat exchanger 1B comprises a heat exchanger housing 5. The heatexchanger housing 5 is nearly in a cylindrical form having upper andlower closed ends. The interior of the heat exchanger housing 5 forms ablood chamber 50. The heat exchanger housing 5 is formed with a tubularheating medium inlet port 52 and a heating medium outlet port 53, bothof which project from the lower end (lower surface) of the heatexchanger housing 5. Meanwhile, a tubular blood inlet port 51 projectsin the lower portion (lower left region in FIG. 2) of the heat exchangerhousing 5. The blood inlet port 51 has a lumen communicating with theblood chamber 50.

Arranged in the interior of the heat exchanger housing 5 is a heatexchange element 54 that is wholly cylindrical in form, a heating mediumchamber-forming member (cylindrical wall) 55 possessing a cylindricalform and provided along the inner periphery of the heat exchange element54, and a partitioning wall 56 separating the inner space of the heatingmedium chamber-forming member 55 into an inlet heating medium chamber 57and an outlet heating medium chamber 58. The heating mediumchamber-forming member 55 forms a heating medium chamber thattemporarily stores the heating medium at the inside of the heat exchangeelement 54 and helps prevent the cylindrical heat exchange element fromdeforming.

The heating medium chamber-forming member 55 and the partitioning wall56 are fixed in the heat exchanger housing 5 by joining, for example byfusion or an adhesive. The heating medium chamber-forming member 55 andthe partitioning wall 56 may be formed as separate members or as aone-piece single unitary body.

The heating medium chamber-forming member 55 is provided with verticallyextending strip-formed openings 59 a, 59 b that penetrate the wall ofthe heating medium chamber-forming member 55. The openings 59 a, 59 bare arranged at diametrically opposite positions on opposite sides ofthe partitioning wall 56 as shown in FIG. 3. The opening 59 acommunicates with the inlet heating medium chamber 57 while the opening59 b communicates with the outlet heating medium chamber 58.

In the illustrated version, the heat exchange element 54 is in the formof a so-called bellows-type heat exchange element (bellows tube) asshown in FIG. 2. The bellows-type heat exchange element 54 comprises abellows-formed central portion and a cylindrical portion at each end(upper and lower ends). The bellows-formed central portion is comprisedof a multiplicity of hollow annular projections that are parallel(inclusive of nearly parallel) to one another so as to form a pluralityof closely arranged undulations. The inner diameter of each cylindricalend portion is equal to (inclusive of nearly equal to) the innerdiameter of the bellows-formed central portion. The heat exchangeelement 54 is formed of a metal material such as stainless steel oraluminum, or a resin material such as polyethylene or polycarbonate, forexample. It is preferable to use a metal material, such as stainlesssteel or aluminum for reasons of strength and heat exchange efficiency.It is particularly preferable to construct the heat exchange element 54as a metal-made bellows tube in a corrugated form having a multiplicityof repetitive concavo-convex portions nearly orthogonal to the axis ofthe heat exchange element 54.

The heat exchanger housing 5, the heating medium chamber-forming member55 and the partitioning wall 56 are of a material, e.g. polyolefin suchas polyethylene or polypropylene, an ester resin (e.g. polyester such aspolyethylene terephthalate or polybutylene terephthalate), a styreneresin (e.g. polystyrene, MS resin or MBS resin), a resin material suchas polycarbonate, a ceramics material of various kinds or a metalmaterial.

Referring to FIGS. 1 to 3, set forth below is a description of the flowof heating medium in the heat exchanging part 1B of the oxygenator 1.The heating medium passing through the heating medium inlet port 52first flows into the inlet heating medium chamber 57 and then to theouter peripheral side of the heating medium chamber-forming member 55via the opening 59 a, thus spreading over the entire periphery of theheating medium-chamber forming member 55 and going into a multiplicityof recesses of the bellows (to the inside of hollow annular projections)of the heat exchange element 54. This heats up or cools down the heatexchange element 54 in contact with the heating medium. Thus, heatexchange (heating or cooling) is effected with the blood flowing at theouter peripheral side of the heat exchange element 54.

The heating medium, served for heating or cooling the heat exchangeelement 54, enters the outlet heating medium chamber 58 through theopening 59 b and then exits at the heating medium outlet port 53.

Although the oxygenator described above and illustrated in the drawingfigures includes the heat exchanging part 1B, it is to be understoodthat the heat exchanger part 1B is not required, and the oxygenator part1A can be used independently of the heat exchanger part 1B.

Referring to FIGS. 1 to 4, the following is a description of the bloodflow in the oxygenator 1 of this embodiment.

In the oxygenator 1, the blood coming through the blood inlet port 51,flows into the blood chamber 50, i.e. between the inner peripheralsurface of the heat exchanger housing 5 and the heat exchange element54, where it contacts the outer surface of the plurality of hollowannular projections of the heat exchange member 54, thus effecting heatexchange (heating or cooling). The blood thus heat exchanged gathers ata downstream portion of the blood chamber 50 and then flows into thehousing 2 of the oxygenating part 1A through the blood inlet aperture24.

The blood passing through the blood inlet aperture 24 flows downstreamalong the blood passage 33 formed in the gaps between the hollow fibermembranes 31. Meanwhile, the gas (gas containing oxygen), suppliedthrough the gas inlet port 26 is distributed by the gas inlet chamber261 into the gas passages 32, i.e., the lumens of the hollow fibermembranes 31. After passing through the gas passages 32, the gas iscollected in the gas outlet chamber 271 and allowed to exit at the gasoutlet port 27. The blood, flowing along the blood passage 33 contactsthe surfaces of the hollow fiber membranes 31 so that gas exchange(oxygenation, and carbon dioxide removal) can be carried out with thegas flowing through the gas passages 32.

In the event bubbles are present in the gas-exchanged blood, the bubblesare caught by the filter member 4 and not allowed to flow downstream ofthe filter member 4. The bubbles caught at the filter member 4 gather orare stopped at the upstream side of the filter member 4 where they enterthe lumens (gas passages 32) of the hollow fiber membranes 31 via themultiplicity of fine pores formed in the wall of the hollow fibermembranes 31. The bubbles are then discharged at the gas outlet port 27together with the gas flowing through the gas passage 32.

The blood thus subjected to gas exchange and bubble removal flows intothe blood outlet aperture 25 where it flows down the blood outletaperture 25 and exits at the blood outlet port 28.

In the oxygenator 1 of this embodiment, it is preferable to make thesurfaces contacted with blood (e.g., the inner surface of the housing 2,the inner surface of the heat exchanger housing 5, the surface of theheating medium chamber-forming member 55, the surface of thepartitioning wall 56, the setting member 7, and the surfaces of thepartitioning walls 8, 9 facing the blood passage 33) antithrombotic. Theantithrombotic surface can be formed by coating and fixing anantithrombotic material over the surface. The antithrombotic materialincludes heparin, urokinase, HEMA-St-HEMA copolymer, poly-HEMA and soon.

In the oxygenator 1, the flow rate of blood through the blood inlet port51 is not especially limited because it is different depending uponpatient's physique and operation scheme. However, usually, some 0.1-2.0L/min is preferred in infant or child, some 2.0-5.0 L/min is preferredin child in elementary or middle school, and some 3.0-7.0 L/min ispreferred in adult.

In the oxygenator 1, the flow rate of the gas supplied through the gasinlet port 26 is not especially limited because it may differ or varydepending upon, for example, a patient's physique and operation scheme.However, usually, 0.05-4.0 L/min is a preferred gas flow rate in infantsor younger children, while 1.0-10.0 L/min is a preferred gas flow ratefor children in elementary or middle school, and 1.5-14.0 L/min is apreferred gas flow rate for adults.

The oxygen concentration in the gas supplied through the gas inlet port26 is also not particularly limited because it is different dependingupon the metabolic amount of oxygen/carbon-dioxide gas of a patientunder operation. However, an example is 40-100%.

The maximum continuous operation time of the oxygenator 1 is not limitedto a specific time because it may differ depending upon, for example,the patient's condition and operation scheme. However, a usual time isapproximately 2-6 hours. The maximum continuous operation time of theoxygenator 1 will rarely amount to a time as long as nearly 10 hours.

The oxygenator illustrated and described here is not limited to all ofthe specific features and details described above and illustrated in thedrawing figures as various features and elements constituting theoxygenator can be replaced with others that are generally suited toexhibiting similar operations or functions.

For example, different structures from those illustrated can be appliedto the structure or form of the connection between the housing 2 and theheat exchanger housing 5, the position and projecting direction of thegas inlet port 26, the gas outlet port 27, the blood outlet port 28,etc. into and out of the housing 2, and the position and projectingdirection of the blood inlet port 51, the heating medium inlet port 52and the heating medium outlet port 53 into and out of the heat exchangerhousing 5. Similarly, the position of the oxygenator 1 in use(positional relationship of various elements relative to the verticaldirection) is not limited to that illustrated.

Thus, it is to be recognized that the principles, preferredembodiment(s) and modes of operation have been described in theforegoing specification, but the invention which is intended to beprotected is not to be construed as limited to the particularembodiment(s) disclosed. Further, the embodiment(s) described herein isto be regarded as illustrative rather than restrictive. Variations andchanges may be made by others, and equivalents employed, withoutdeparting from the spirit of the present invention. Accordingly, it isexpressly intended that all such variations, changes and equivalentswhich fall within the spirit and scope of the present invention asdefined in the claims, be embraced thereby.

What is claimed is:
 1. A method of performing gas exchange for bloodcomprising: introducing blood into a blood inlet of a housing in whichare positioned a plurality of hollow fiber membranes each having a lumenin communication with a gas inlet and a gas outlet so that the bloodflows outside the lumens of the hollow fiber membranes toward a bloodoutlet; introducing gas into the lumens of the hollow fiber membranes tosubject the blood flowing outside the lumens of the hollow fibermembranes to gas exchange; removing bubbles in the blood after the bloodhas been subjected to the gas exchange and before the blood isdischarged from the housing by way of the blood outlet, the removing ofthe bubbles occurring as a result of the blood which has been subjectedto the gas exchange passing through a filter member which has a planarsurface in direct contact with the hollow fiber membranes; anddischarging the blood which has been subjected to the gas exchange andwhich has passed through the filter member from the housing by way ofthe blood outlet.
 2. The method according to claim 1, wherein the bloodwhich has passed through the filter member flows through a gap betweenthe filter member and an inner surface of the housing before beingdischarged from the housing by way of the blood outlet.
 3. The methodaccording to claim 1, further comprising introducing the blood into aheat exchanger, and discharging the blood from the heat exchanger beforeintroducing the blood into the blood inlet.
 4. The method according toclaim 1, further comprising passing the blood through a heat exchangerbefore introducing blood into the blood inlet.
 5. A method of performinggas exchange for blood comprising: introducing blood into a blood inletof a rectangular shape housing in which are positioned a plurality ofhollow fiber membranes each having a lumen in communication with a gasinlet and a gas outlet so that the blood flows outside the lumens of thehollow fiber membranes toward a blood outlet; introducing gas into thelumens of the hollow fiber membranes to subject the blood flowingoutside the lumens of the hollow fiber membranes to gas exchange;catching bubbles in the blood after the blood has been subjected to thegas exchange and before the blood is discharged from the housing throughthe blood outlet, the bubbles being caught by virtue of the blood whichhas been subjected to the gas exchange passing through a bubble catchingfilter member; the bubbles caught by the bubble catching filter memberentering the lumens of the hollow fiber membranes and being dischargedout of the housing by way of the gas outlet; and discharging the bloodwhich has been subjected to the gas exchange and which has passedthrough the bubble catching filter member out of the housing by way ofthe blood outlet.
 6. The method according to claim 5, wherein the bloodwhich has passed through the filter member flows through a gap betweenthe filter member and an inner surface of the housing before beingdischarged from the housing by way of the blood outlet.
 7. The methodaccording to claim 5, further comprising introducing the blood into aheat exchanger, and discharging the blood from the heat exchanger beforeintroducing the blood into the blood inlet.
 8. The method according toclaim 5, further comprising passing the blood through a heat exchangerbefore introducing blood into the blood inlet.
 9. The method accordingto claim 5, wherein the bubble catching filter member through which theblood passes is in direct contact with the hollow fiber membranes. 10.The method according to claim 5, wherein the bubble catching filtermember through which the blood passes has a planar surface in directcontact with the hollow fiber membranes.
 11. A method of performing gasexchange for blood comprising: introducing blood into an inlet of arectangular shape housing in which are positioned a plurality of hollowfiber membranes each having a lumen in communication with a gas inletand a gas outlet so that the blood flows exteriorly of the hollow fibermembranes toward a blood outlet; introducing gas into the lumens of thehollow fiber membranes to subject the blood flowing exteriorly of thehollow fiber membranes to gas exchange; discharging the blood which hasbeen subjected to the gas exchange from the housing by way of the bloodoutlet; and removing bubbles in the blood in the housing after the bloodhas been subjected to the gas exchange and before the blood isdischarged from the housing by way of the blood outlet.
 12. The methodaccording to claim 11, wherein the bubbles are removed by passing theblood which has been subjected to the gas exchange through a bubblefilter.
 13. The method according to claim 12, wherein the blood whichhas passed through the bubble filter flows through a gap between thebubble filter and an inner surface of the housing before beingdischarged from the housing by way of the blood outlet.
 14. The methodaccording to claim 11, further comprising introducing the blood into aheat exchanger, and discharging the blood from the heat exchanger beforeintroducing the blood into the blood inlet.
 15. The method according toclaim 11, further comprising passing the blood through a heat exchangerbefore introducing blood into the blood inlet of the housing.
 16. Themethod according to claim 11, further comprising discharging the bubbleswhich have been removed from the blood out of the housing by conveyingthe bubbles through the lumens of the hollow fiber membranes and throughthe gas outlet.